The overall long-term objectives of this research are to elucidate mechanisms by which cell surface metalloproteinases and their secreted counterparts are regulated and interact, activate and degrade peptides and proteins at the cell surface and extracellularly, as well as to define the roles of these proteases in health and diseases such as kidney and urinary tract disease. The work has led to the discovery and characterization of meprins, complex and unique mammalian metalloproteinases abundantly expressed at the brush border membrane of kidney and intestinal epithelial cells, and in leukocytes under certain conditions. The hypothesis is that meprins have a protective role in host defense in urinary tract infections, but that the alpha/beta form is actively involved in the pathophysiology of acute renal injury. In the next period, the Specific Aims are to: (1) Determine whether meprin alpha/beta is damaging to specific proteins in kidney epithelial cells in response to hypoxia or ischemia-reperfusion. Immunohistochemical, immunoprecipitation, and proteomic techniques will be used with kidneys and proximal tubules from wild-type and meprin knockout mice to identify specific targets of meprin interaction and hydrolysis in brush border membrane, cytosol and extracellular compartments. (2) Determine whether leukocytic meprins affect movement and activity of these inflammatory cells to ischemic kidney and enhance damage. Bone marrow cells from wild-type and meprin knockout mice will be destroyed by radiation, and replaced by donor leukocytes from wild-type or meprin knockout mice carrying a green- fluorescent protein. The movement of the donor leukocytes to kidneys in the chimeric mice subjected to ischemia-reperfusion, and the injury caused by meprin positive and negative leukocytes will give insight into the damage caused by these cells. (3) Determine whether meprin alpha secreted from the kidney, or leukocytic meprins, affect the establishment and severity of urinary tract disease. Mice of different meprin genotypes will be infected with uropathic bacteria in the bladder, and the susceptibility to bladder and kidney infections will be determined. The roles of leukocytic and kidney meprins will be assessed using the chimeric mice. The activation of meprins at sites of infection, concentrations of active beta-defensins, and interactions of meprin isoforms with bacteria will be assessed to gain insights into mechanisms of protection. The availability of the meprin alpha and beta knockout mice are unique resources for these studies, and fundamental knowledge of these metalloproteinases will lead to new concepts, treatments, and interventions for kidney and urinary tract diseases.